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Recreating the Intense Conditions of the Earth’s Mantle Solves A Long-standing Geological Mystery

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inner earth

The various layers of the inner Earth. (Credit: Ellen Bronstayn/Shutterstock)

Science is never exactly easy, but it’s especially tough when you can’t see, touch or even really interact with your subject. Consider the plight of a geophysicist interested in the makeup and structure of Earth’s interior. Without being able to dig up a sample of our planet’s ultrahot, ultra-pressurized mantle, how can they figure out what makes our planet work?

The answer, in part, is seismic waves. When the ground shakes, as in an earthquake, the vibrations go through and interact with all the materials in their way. This can provide scientists with a means of imaging all those materials, allowing them to virtually peer beneath the surface.

But sometimes that’s not enough. If the models tell you the vibrations — analogous to sound waves in some cases — should travel at a certain speed, but the data show they don’t, you’re left with an anomaly. Something’s wrong, but without somehow recreating the incredible conditions hundreds of miles below the surface, how can you figure out what?

Just such an issue has been plaguing geophysicists studying the Earth’s innards, who’ve noticed that vibrations from earthquakes traveling through the mantle have been going slower than they should be.

At least until now, that is. According to a Nature paper this week, a team of Japanese scientists figured out what was wrong just by recreating those crazy conditions after all.

Mantle Pieces

Their work all comes down to a specific mineral, calcium silicate (CaSiO3) arranged in what’s called a perovskite structure. Scientists refer to this as calcium silicate perovskite, or simply CaPv. This mineral is a major part of Earth’s mantle, the vast region between surface and the inner core.

The mantle itself is divided into the upper and lower, and the boundary between the two, around 410 miles down, is still somewhat mysterious to scientists. That’s where they’d been finding some of these anomalous velocities for traveling sound waves. One idea was maybe the reason the measurements weren’t lining up with the models was because they didn’t fully understand how the CaPv behaved within the mantle. But it’s hard to know for sure if that’s the case, because in those infernally hot temperatures, CaPv takes on a cubic structure, which breaks down into other forms at temperatures below about 600 kelvin.

As the authors put it, “Despite its importance, no measurements of sound velocities have been made in cubic CaPv at high temperature, because this phase is unquenchable at ambient conditions and hence there is no adequate sample for such measurements.”

So, basically, they just made some.

Mineral Madness

The researchers synthesized some cubic CaPv from a glass rod, and kept it at temperatures up to 1700 K and pressures of up to 23 billion pascal (for reference, standard air pressure is 101,000 pascal). The mineral maintained its cubic form in these extreme conditions, allowing the team to run ultrasonic sound velocity measurements.

They found that the material really doesn’t behave the way the theories had predicted: CaPv is about 26 percent less rigid than expected, so sound waves would in fact travel more slowly through it than expected — just as had been observed.

Not only does the finding resolve the conflict between mantle models and experimental data, but it also supports another intriguing idea: This region between the upper and lower mantle may be home to subducted oceanic crust — parts of the ocean floor forced into the mantle — rife with CaPv.

“These results could contribute to our understanding of the existence and behavior of subducted crust materials in the deep mantle,” the authors write, and they also suggest new research avenues for directly measuring the velocity of seismic waves through mantle materials.

Slowly but surely, scientists are figuring out better ways to look at and understand the invisible depths beneath Earth’s surface.

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Ecology

Today’s letters: ‘Visionary’ plans don’t always work in Ottawa

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The opinion piece written by Tobi Nussbaum, CEO of the NCC, declares that a “bold, visionary transit plan” would showcase the capital.

As a long-term resident of Ottawa, I’ve had it with visionary plans. In the 1950s, the streetcars serving Ottawa so well were sent to the scrapyards. In the early ’60s, Queensway construction bulldozed established neighbourhoods and ripped the city apart. Later in the decade, the downtown railway station, which could have formed the hub of a commuter network, was relocated to the suburbs. These actions, in the name of “progress,” were undertaken with the “vision” to make Ottawa a car-reliant city.

Now we have an LRT, built just in time for most people to realize that they do not have to go downtown as they can work from home.

Current thinking is pushing a new “link” between Ottawa and Gatineau, with yet more expensive and disruptive infrastructure projects being touted, including a tramway or another tunnel under the downtown core.

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Ecology

That was then: Biggest earthquake since 1653 rocked Ottawa in 1925

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A regular weekly look-back at some offbeat or interesting stories that have appeared in the Ottawa Citizen over its 175-year history. Today: The big one hits.

The Ottawa Senators were playing a Saturday night game against the Montreal Canadiens at the Auditorium, the score tied 0-0 halfway through the second period. Sens’ rookie Ed Gorman and the Habs’ Billy Boucher had just served penalties for a dustup when the building began to make “ominous creaking sounds.” A window crashed to the ground.

Nearby, at Lisgar Collegiate, all eyes were on teenager Roxie Carrier, in the role of Donna Cyrilla in the musical comedy El Bandido. She had the stage to herself and was singing “Sometime” when the building rocked, the spotlight went out, and someone in the audience yelled “Fire!”

At a home on Carey Avenue, one woman’s normally relaxed cat suddenly arched its back, rushed around the room two or three times, spitting angrily, and climbed up the front-window curtains.

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Ecology

Ottawa delays small nuclear reactor plan as critics decry push for new reactors

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TORONTO — Canadians will have to wait a little while longer to see the federal government’s plan for the development of small nuclear reactors, seen by proponents as critical to the country’s fight against global warming.

Speaking at the opening of a two-day virtual international conference on Wednesday, the parliamentary secretary to the minister of natural resources said the plan will lay out key actions regarding the reactors. Its launch, Paul Lefebvre said, would come in the next few weeks.

“We’re still putting the finishing touches on it,” Lefebvre said. “The action plan is too important to be rushed.”

Small modular reactors — SMRs — are smaller in size and energy output than traditional nuclear power units, and more flexible in their deployment. While conventional reactors produce around 800 megawatts of power, SMRs can deliver up to 300 megawatts.

Proponents consider them ideal as both part of the regular electricity grid as well as for use in remote locations, including industrial sites and isolated northern communities. They could also play a role in the production of hydrogen and local heating.

“SMRs will allow us to take a bold step of meeting our goal of net-zero (emissions) by 2050 while creating good, middle class jobs and strengthening our competitive advantage,” said Lefebvre.

Natural Resources Minister Seamus O’Regan had been scheduled to speak at the conference but did not due to a family emergency.

Industry critics were quick to pounce on the government’s expected SMR announcement. They called on Ottawa to halt its plans to fund the experimental technology.

While nuclear power generation produces no greenhouse gas emissions, a major problem facing the industry is its growing mound of radioactive waste. This week, the government embarked on a round of consultations about what do with the dangerous material.

Dozens of groups, including the NDP, Bloc Quebecois, Green Party and some Indigenous organizations, oppose the plan for developing small modular reactors. They want the government to fight climate change by investing more in renewable energy and energy efficiency.

“We have options that are cheaper and safer and will be available quicker,” Richard Cannings, the NDP natural resources critic, said in a statement.

Lefebvre, however, said the global market for SMRs is expected to be worth between $150 billion and $300 billion a year by 2040. As one of the world’s largest producers of uranium, Canada has to be part of the wave both for economic and environmental reasons, he said.

“There’s a growing demand for smaller, simpler and affordable nuclear technology energy,” Lefebvre said.

Joe McBrearty, head of Canadian Nuclear Laboratories, told the conference the company had signed a host agreement this week with Ottawa-based Global First Power for a demonstration SMR at its Chalk River campus in eastern Ontario. A demonstration reactor will allow for the assessment of the technology’s overall viability, he said.

“When talking about deploying a new technology like an SMR, building a demonstration unit is vital to the success of that process,” McBrearty said. “Most importantly, it allows the public to see the reactor, to kick the tires so to speak, and to have confidence in the safety of its operation.”

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